Sepsis facilitates brain serotonin activity and impairs learning ability in rats

Sepsis often provokes various neurological disorders. Because many neurolog ic symptoms are caused by changes in neurotransmissions, we investigated th e relationship between behavioral alterations and changes in activities of the monoaminergic systems in rats. Sepsis was induced by cecal ligation and puncture. A step-through passive avoidance test was used for the behaviora l evaluation. Passive avoidance retention in animals subjected to learning immediately before the septic or sham operation was examined after 24 or 48 h. Retention performance in animals subjected to learning 24 h after the o peration was also examined after a further 24 h, Plasma concentrations of a mino acids were determined 24 h after the operation. The activities of the brain monoaminergic systems were evaluated by ratios of metabolites to mono amines. Marked damage was found in the septic rats in the blood analysis 24 h after the operation. The plasma concentrations of tyrosine and arginine in the septic rats were decreased to 69% and 70% of those in the sham-opera ted animals, respectively. Retention performance was impaired in the septic rats when they were subjected to learning 24 h after the operation, but it was not impaired when animals were subjected to learning before the septic operation. The brain concentration of serotonin was increased in the cereb ral cortex, striatum, and hippocampus 48 h after the septic operation, but not after 24 h. The concentration of 5-hydroxyindoleacetic acid, a metaboli te of serotonin, was increased in the above three regions both 24 and 48 h after the operation, but not in the hypothalamus. Facilitation of the serot onergic activity in the telencephalon and hippocampus is suggested to be in volved in the impairment of learning ability in sepsis. (C) 1999 Elsevier S cience B.V. All rights reserved.